Energy, Work, and Simple Machines

Transcription

1 CHAPTER 3 Energy, Work, and Simple Machines Types of Energy What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Key Concepts What is? LESSON 1 What are the different forms of? How is used? Before Statement After 1. Energy is the ability to produce motion. 2. Waves transfer from place to place. What is? You probably have heard the word used on television, the radio, or the Internet. Commercials claim that the newest models of cars are efficient. What is? Scientists define as the ability to cause a change. Using this definition, what does have to do with cars? Most cars use some type of fuel, such as gasoline or diesel, as their source. A car s engine transforms the stored in the fuel to a form of that moves the car. Compared to other cars, the car that is efficient uses less fuel to make the car move a certain distance. Gasoline and diesel fuel are not the only sources of. Food is an source for your body. Also, satellites need a source of to run their systems and to stay in orbit. Solar panels provide for the International Space Station. As you will read, wind, coal, nuclear fuel, Earth s interior, and the Sun also are sources of. Energy from each of these sources can be transformed into other forms of, such as electric. Every time you turn on a light, you use that was transformed from one form to another. Create a Quiz Create a quiz about types of. Exchange quizzes with a partner. After taking the quizzes, discuss your answers. Read more about the topics you don t understand. Key Concept Check 1. Define What is? Reading Essentials Energy, Work, and Simple Machines 39

2 Make a vertical 3 4 folded table to organize your notes about the different types of in each category. Types of Energy Kinetic Potential Energy for Waves Examples Notes 2. Assess What is one drawback of wind? 3. Explain What creates an electric current? Kinetic Energy You just turned the page of this book. As the page was moving, it had kinetic the an object has because it is in motion. Anything that is in motion has kinetic, including large objects that you can see as well as small particles, such as molecules, ions, atoms, and electrons. Kinetic Energy of Objects Huge wind turbines on wind farms use wind as a source of. When the wind blows, the large blades of the wind turbines turn. Because the blades are moving, they have kinetic. Kinetic depends on mass. If the turbine blades were smaller and had less mass, they would have less kinetic. Kinetic also depends on speed. When the wind blows harder, the blades move faster. The faster the blades move, the more kinetic they have. When the wind stops, the blades stop. When the blades are not moving, the kinetic of the blades is zero. One of the drawbacks of using wind-generated is that wind does not always blow. As a result, wind provides an inconsistent supply of. Electric Energy When you turn on a lamp or use a cell phone, you are using a type of kinetic electric. Recall that all objects are composed of atoms. Electrons move around the nucleus of an atom, and they move from one atom to another. When electrons move, they have kinetic and create an electric current. The that an electric current carries is a form of kinetic called electric. Electric can be produced by moving objects. When the blades of the wind turbines rotate, they turn a generator. The generator changes the kinetic of the moving blades into electric. Electric generated from the kinetic of wind is a clean source of because it creates no waste products. Potential Energy Suppose you hold up a piece of paper. When the paper is held above the ground, it has potential. Potential is stored that depends on the interaction of objects, particles, or atoms. 40 Energy, Work, and Simple Machines Reading Essentials

3 Gravitational Potential Energy Gravitational potential is a type of potential stored in an object due to its height above Earth s surface. The water at the top of a dam has gravitational potential because it is higher above the surface of Earth than the water at the base of the dam. Gravitational potential depends on the mass of an object and its distance from Earth s surface. The more mass an object has and the greater its distance from Earth, the greater its gravitational potential. In a hydroelectric plant, water above a dam flows through turbines as it falls. Generators connected to the spinning turbines convert the gravitational potential of the water into electric. Hydroelectric plants are a very clean source of. About 7 percent of all electric power in the United States is produced from hydroelectric. However, hydroelectric plants can interrupt the movement of animals in streams and rivers. Chemical Energy Most electric in the United States comes from fossil fuels such as petroleum, natural gas, and coal. Chemical bonds join the atoms that make up these fossil fuels. Chemical bonds have the potential to break apart. Therefore, chemical bonds have a form of potential called chemical. Chemical is that is stored in and released from the bonds between atoms. When an plant burns fossil fuels, the chemical bonds between the atoms break apart. When this happens, chemical transforms to thermal. The plant uses this thermal to heat water and form steam. The steam turns a turbine, which is connected to a generator that generates electric. A drawback of fossil fuels is that they introduce harmful waste products, such as sulfur dioxide and carbon dioxide, into the environment. Sulfur dioxide in the air creates acid rain. Most scientists suspect that increased levels of carbon dioxide in the atmosphere contribute to climate change. Scientists are searching for replacement fuels. Fossil fuels are not the only source of chemical. Chemical also is stored in the foods you eat. Your body converts the stored in chemical bonds in food into the kinetic of your moving muscles and into the electric that sends signals through your nerves to your brain. 4. Apply Assume your science book and math book have the same mass. Your science book is on the top shelf of your bookcase, and your math book is on the bottom shelf. Which has the most gravitational potential? Why? 5. State What is chemical? 6. Recognize List three sources of food that you have eaten recently. Reading Essentials Energy, Work, and Simple Machines 41

4 7. Differentiate How does nuclear fission differ from nuclear fusion? 8. Name What types of combine and form mechanical? 9. Distinguish How does thermal differ from mechanical? Nuclear Energy Most on Earth comes from the Sun. A process in the Sun called nuclear fusion joins the nuclei of atoms. Nuclear fusion releases large amounts of. On Earth, nuclear plants use the potential stored in the nuclei of atoms to produce electric. In these plants, the nuclei of certain atoms break apart using a process called nuclear fission. Both nuclear fusion and nuclear fission release nuclear stored in and released from the nucleus of an atom. Nuclear fission produces a large amount of from just a small amount of fuel. However, the process produces radioactive waste that is hazardous and difficult to dispose of safely. Kinetic and Potential Energies Combined Recall that a moving object has kinetic. Objects such as wind turbine blades and particles, such as molecules, ions, atoms, and electrons, often have kinetic and potential energies. Mechanical Energy The sum of potential and kinetic in a system of objects is mechanical. Mechanical is the a system has because of the movement of its parts (kinetic ) and because of the position of its parts (potential ). An object, such as a wind turbine, has mechanical because the parts that make up the system have both potential and kinetic. A rotating blade has kinetic because of its motion. It also has gravitational potential because of its distance from Earth s surface. Thermal Energy The particles that make a wind turbine also have thermal. Thermal is the sum of the kinetic and potential of the particles that make up an object. Although you cannot see the individual particles move, they vibrate back and forth in place. This movement gives the particles kinetic. The particles also have potential because of the distance between particles and the charge of the particles. 42 Energy, Work, and Simple Machines Reading Essentials

5 Geothermal Energy The particles in Earth s interior contain great amounts of thermal. This is called geothermal. Geothermal plants use this thermal to heat water and turn it to steam. The steam turns turbines in electric generators, converting the geothermal to electric. Geothermal produces almost no pollution. However, geothermal plants must be built in places where molten rock is close to Earth s surface. Energy from Waves Have you ever seen waves crash on a beach? When a big wave crashes, you hear the sound of the impact. The movement and the sound result from the carried by the wave. Waves are disturbances that carry from one place to another. Waves move only, not matter. Sound Energy Clapping your hands together creates a sound wave in the air. Sound waves move through matter. Sound is carried by sound waves. Some animals, such as bats, emit sound waves to find their prey. The length of time it takes sound waves to travel to a bat s prey and then echo back tells the bat the location of its prey. Seismic Energy You probably have seen news reports showing photographs of damage caused by earthquakes. Earthquakes occur when Earth s tectonic plates, or large portions of Earth s crust, suddenly shift position. The kinetic of the plate movement is carried through the ground by seismic waves. Seismic is the transferred by waves moving through the ground. Seismic can destroy buildings and roads. Radiant Energy When you listen to the radio, use a lamp, or talk on your cell phone, do you think of waves? Electromagnetic waves are electric and magnetic waves that move perpendicular to each other, as shown in the figure at right. Electromagnetic Waves Direction of travel Magnetic field Electric field Electron 10. Identify What is the source of geothermal? Visual Check 11. Identify Highlight the magnetic field that occurs next to the electric field. Key Concept Check 12. Name What are the different forms of? Reading Essentials Energy, Work, and Simple Machines 43

6 Forms of Electromagnetic Waves Visible light waves Infrared waves (thermal emitted from body as waves) Radio waves Microwaves Solar cell (transforms radiant to electric ) Infrared waves (used by computer to read compact disc) Microwaves Visual Check 13. Name What type of electromagnetic waves does a cell phone use? Key Concept Check 14. Summarize How is radiant used? Radio waves, light waves, and microwaves are all electromagnetic waves, as shown in the figure above. Some electromagnetic waves can travel through solids, liquids, gases, and vacuums. The carried by electromagnetic waves is radiant. Electromagnetic waves transmit the Sun s to Earth. Photovoltaic (foh toh vohl TAY ihk) cells, also called solar cells, are made of special material that transforms the radiant of light into electric. You might have used a solar calculator. It does not need batteries because it has a photovoltaic cell. Photovoltaic cells also are used to provide to satellites, offices, and homes. Because so much sunlight hits the surface of Earth, the supply of solar is plentiful. Also, using solar as a source for electric produces almost no waste or pollution. However, only about 0.1 percent of the electric used in the United States comes directly from the Sun. 44 Energy, Work, and Simple Machines Reading Essentials

7 Mini Glossary chemical : that is stored in and released from the bonds between atoms electric : a form of kinetic that an electric current carries : the ability to cause a change kinetic : the an object has because it is in motion mechanical : the sum of potential and kinetic in a system of objects potential : stored that depends on the interaction of objects, particles, or atoms radiant : the carried by electromagnetic waves seismic : the transferred by waves moving through the ground sound : carried by sound waves thermal : the sum of the kinetic and potential of the particles that make up an object nuclear : stored in and released from the nucleus of an atom 1. Review the terms and their definitions in the Mini Glossary. Write a sentence describing the source of seismic. 2. Write the type of next to each clue in the graphic organizer. kinetic of motion from moving electrons stored carried by electromagnetic waves from shifting tectonic plates carried by sound waves thermal inside Earth What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? Types of Energy thermal the kinetic and potential of particles ConnectED Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. mechanical from a system of objects stored in bonds between atoms released from the nuclei of atoms from an object s height above Earth s surface END OF LESSON Reading Essentials Energy, Work, and Simple Machines 45